Study of unitary Bose polarons with Diffusion Monte-Carlo and Gross-Pitaevskii approaches

We present a detailed study of the properties of unitary Bose polarons, i.e., impurities strongly interacting with a bath of dilute bosons via a short-range potential with infinite scattering length. Through a comparison with Diffusion Monte-Carlo calculations, we demonstrate that the Gross-Pitaevskii theory accurately describes the properties of a heavy impurity if the gas parameter remains small everywhere in the system, including the vicinity of the impurity. Furthermore, we investigate the effects of the finite range of the bath-bath interaction potential by means of a non-local extension of the Gross-Pitaevskii equation and we discuss the applicability of the Born approximation.